The present invention relates to a chip-type battery comprising a plurality of power generating elements which are stacked, each element containing a sintered material.
As electronic devices become more and more compact, more electronic components are constructed in the form of chips and they are densely mounted on printed circuit boards. Usually, the electronic components are mounted by reflow soldering. With the increased demand for lead-free electronic devices in recent years, lead-free soldering has become popular for use. Lead-free soldering requires a reflow temperature of about 240° C., which is higher than the conventional reflow temperature of about 200° C. Under the circumstances, electrolytic capacitors containing an electrolyte have gradually been replaced with chip-type all solid state electrolytic capacitors. In addition to this, there are proposed chip-type batteries that can be directly mounted on substrates (Japanese Laid-Open Patent Publication No. Hei 6-231796).
Electrochemical devices such as electrolytic capacitors and batteries have a polarity. Accordingly, when they are used, it is necessary to identify a cathode, or positive electrode, and an anode, or negative electrode. For example, if the polarity of a terminal cannot be identified when an electrochemical device having a polarity is mounted on a substrate, the electrochemical device might be mounted with the anode and the cathode reversed.
FIG. 1 is a perspective view of a typical chip-type electrochemical device. This chip-type electrochemical device has a symmetric structure, and comprises a body 11 having a substantially rectangular parallelepiped shape, a first terminal 12 and a second terminal 13, each terminal arranged at the end of the body 11. This type of shape is adopted into multilayer ceramic capacitors, functional polymer electrolytic aluminum capacitors, etc, which have been commercialized.
Multilayer ceramic capacitors do not have a polarity, and therefore there is no need to identify a first terminal and a second terminal. Functional polymer electrolytic aluminum capacitors and tantalum capacitors, however, do have a polarity, and therefore a first terminal and a second terminal must be identified.
In view of this, in order to identify a first terminal and a second terminal, there is proposed to print, with the use of an ink, a mark 24 for indicating the polarity of a first terminal 22 or a second terminal 23 on a body 21 of an electrochemical device as shown in FIG. 2. Such a mark, however, is not applicable to electrochemical devices produced through sintering process. This is because, since the mark should be printed in the early stages of the production process and the sintering process is usually performed in the latter stages of the production process, the mark printed using an ink is evaporated during the sintering process.
Meanwhile, some electrochemical devices not having a stacked structure have an asymmetric structure with a first terminal and a second terminal of different shapes. A tantalum solid electrolytic capacitor (F95 series manufactured by Nichicon Corporation) shown in FIG. 3, for example, has a cathode terminal 32 and an anode terminal 33 of different shapes arranged at the ends of a body 31. The body 31 comprises a device part 35 and an outer coating resin 36 for covering the device part 35. From the cathode-terminal-side end of the device part 35 is protruded a cathode lead 34. Likewise, a tantalum solid electrolytic capacitor (T491 series manufactured by KEMET Corporation) shown in FIG. 4 is characterized by the shape of the end of a body 41. The body 41 comprises a device part 45 and an outer coating resin 46 for covering the device part 45. The end of the outer coating resin 46 where a cathode terminal 42 is disposed has a different shape from the end of the same where an anode terminal 43 is disposed. It is, however, difficult to adopt the structures described above into electrochemical devices comprising a plurality of power generating elements which are stacked.
Another approach is proposed to address the step of mounting an electrochemical device on a substrate. For example, a solid electrolytic capacitor shown in FIG. 5 is proposed in which a cathode terminal 52 is formed in the center of a body 51 and anode terminals 53 are respectively formed at the ends of the body 51 (Japanese Laid-Open Patent Publication No. Hei 6-232011). Although the purpose is different, there is also proposed a capacitor as shown in FIG. 6 in which a dent 67 is formed at an end of a body 61 having a cathode terminal 62 so that a cathode lead 64 is exposed from the dent 67. Because the cathode terminal 62 has a different shape from an anode terminal 63 in this capacitor, it is easy to identify the polarity (Japanese Laid-Open Patent Publication No. Hei 7-115041). However, in this case also, it is difficult to adopt such a structure into electrochemical devices comprising a plurality of power generating elements which are stacked.
Meanwhile, Japanese Laid-Open Patent Publication No. Hei 11-26297 proposes to house a chip-type capacitor in an outer case 71 having a substantially rectangular parallelepiped shape as shown in FIG. 7. The outer case 71 is provided with an L-shaped first terminal electrode 74 extending from a first side face 72 to a bottom face 73 and an L-shaped second terminal electrode 76 extending from a second side face 75, which is positioned opposite to the first side face 72, to the bottom face 73. The first terminal electrode 74 and the second terminal electrode 76 are formed such that they are in positions displaced from the symmetric position in the outer case 71. The capacitor housed in the outer case 71 is a surface-mounted capacitor using no connecting lead wire. Accordingly, even if an attempt is made to mount it on a circuit board such that the first terminal electrode and the second terminal electrode are reversed, because the position of each terminal on the circuit board does not correspond to that of each electrode on the case, reverse connection can be prevented.
Moreover, Japanese Laid-Open Patent Publication No. Hei 11-26297 proposes to house an electrochemical device in an outer case 81 having a substantially rectangular parallelepiped shape as shown in FIG. 8. The outer case 81 is provided with an L-shaped first terminal electrode 84 extending from a first side face 82 to a bottom face 83 and a second terminal electrode 86 extending from a second side face 85, which is positioned opposite to the first side face 82, to the bottom face 83. In this case, even if the capacitor housed in the outer case 81 is mounted on a circuit board with its polarity reversed, the first terminal electrode 84 and the second terminal electrode 86 do not come in contact with the terminals on the circuit board.
The use of the outer cases as shown in FIGS. 7 and 8, however, requires an increased number of components as well as an increased cost of equipment because it necessitates two different processes: the process to provide the cathode terminal and the process to provide the anode terminal. In other words, the use of the outer cases as shown in the figures is accompanied by the problem of increasing the production cost.
As can be clearly understood from the above, a versatile means for readily identifying a first terminal and a second terminal for a chip-type battery comprising a plurality of power generating elements which are stacked, each element containing a sintered material, has not yet been proposed.